It is well known to use roofing membrane retainers, or seam plates in order to retain roof decking membranes atop roof decking substructures. More particularly, roof decking membranes are of limited width relative to a roof structure, necessitating placement of membranes adjacent or in overlapping arrangement. These constructions are well-known in the art. U.S. Pat. No. 4,945,699 to Murphy illustrates one roofing seam plate suitable for retaining membranes atop a roof decking substructure. Typically, an insulation layer is placed atop a steel roof decking structure, after which membranes are rolled thereatop. A seam plate is applied along the membrane edge with a screw fastener, driving the screw through the insulation panel and into the decking to retain an edge of the membrane therealong. Subsequently, an adjacent membrane edge is adhesively applied over the edge of the adjacent membrane where the seam plate has been applied to the first membrane, completely covering over the seam plate. The construction provided in U.S. Pat. No. 4,945,699 includes a plurality of circumferentially spaced apart prongs or tangs that terminate in a sharp gripping point. The prongs grip the underlying membrane, thereby preventing it from loosening or freeing with respect to the seam plate or the insulation and decking structure provided therebelow. Hence, the membrane and insulation panel are retained by the seam plate and fastener to the underlying steel roof decking despite wind loading to the roof structure that might otherwise raise or rip the membrane and insulation from the roof decking. However, the presence of sharp prongs on a seam plate tends to increase the likelihood that the roofing membrane will puncture or tear when subjected to wind loads or other in-use loads. Secondly, the prongs on such seam plates make installation more difficult as roofing installers retrieve by hand individual seam plates from within a container, or bucket and the prongs tend to cut and abrade their fingers and hands.
Similarly, the seam plate of U.S. Pat. No. 6,665,991 to Hasan utilizes downwardly extending v-shaped projections that each form a pair of side legs at an included angle of 90 degrees. Each v-shaped projection has a corner or apex portion formed at the intersection of the legs. Such v-shaped configuration has two severed edges, one on either side of the v-shaped configuration. Accordingly, two sharp points are still provided by each projection at the corner. Such points tend to increase the likelihood that a membrane will be torn under severe loading conditions which can lead to failure of the fastening system and tearing of the membrane. Secondly, the two corners on each v-shaped projection can also lead to undesirable cutting and abrading of the hands of a roofing installer.
Accordingly, improvements are needed for seam plates and roofing membrane retainers in order to increase the ability of the retainers to grip roofing membranes when subjected to significant loading conditions, while reducing the likelihood that tears and punctures will propagate through the membrane under such loading conditions. Secondly, improvements are needed in order to reduce the likelihood that installers will cut and abrade their hands while retrieving and handling such retainers during an installation operation.